This application is based on Japanese Patent Application No. 9-355439 filed Dec. 24, 1997, the content of which is incorporated herein by reference.
The present invention relates to a display controller and a computer system using the same and, more particularly, to a display controller having a motion picture display function, computer system, and motion picture display control method.
In recent years, along with the development of computers and multimedia techniques, various kinds of so-called multimedia compatible personal computers have been developed. A personal computer of this type has a function of reproducing motion pictures and audio data in addition to text and graphics data.
With the advent of such multimedia computers, a DVD has received a lot of attention as an alternative storage medium to a CD-ROM. A single DVD-ROM medium can record data of about 4.7 Gbytes about seven times the capacity of the existing CD-ROM on one side, and can record data of about 9.4 Gbytes in case of two-sided recording. Using such DVD-ROM media, titles such as movies including a large volume of video information can be reproduced with high quality on the personal computer.
Video information recorded on a DVD-ROM medium consists of two kinds of data, i.e., presentation data and navigation data. The presentation data is a set of video objects to be reproduced, and consists of video, subpicture, and audio data. The video data is compressed and coded by MPEG2. As the coding schemes of subpicture and audio data, runlength coding, DOLBY DIGITAL, and the like are supported. The subpicture data is bitmap data, and is used for displaying superimposed dialogues of a movie, selection items on a menu window, and the like. One video object can contain video data for one channel, audio data for a maximum of eight channels, and subpicture data for a maximum of 32 channels.
The navigation data is reproduction control data for controlling the reproduction sequence of the presentation data, and navigation commands can be embedded in this data. The navigation commands are used for changing the reproduction contents or order of video data. Using the navigation commands, a title creator can define various branch structures in his or her title, and can create an interactive title.
When a motion picture title stored in a DVD is reproduced on a personal computer, an encoded stream of motion picture data is loaded from a DVD drive into the main memory of the personal computer, and the loaded stream is transferred to an MPEG2 decoder. The MPEG2 decoder descrambles the encoded stream, which has been scrambled to prevent the title from being illicitly copied, and then decodes to expand the encoded stream. The decoded motion picture data is sent to a display controller (VGA controller) for controlling the display monitor of the personal computer. The motion picture data sent to the VGA controller is temporarily written in a video RAM like normal graphics data provided by an OS or an application program, and is then displayed on the screen of the display monitor or a TV.
However, the motion picture data stored in the DVD is created based on TV video signals of, e.g., the NTSC scheme as in a home TV, and the vertical sync frequency of the motion picture data decoded by the MPEG2 decoder is normally 60 Hz (60 fields/sec). By contrast, the VGA controller is designed to display at a dedicated refresh rate (60 Hz, 72 Hz, 75 Hz, or the like) for controlling a sequential scan display monitor. The refresh rate used is determined by the screen resolution or the like of the display monitor. Note that the refresh rate represents the number of fields to be refreshed per second, and the quality of the display screen can be improved as the refresh rate becomes higher. Normally, a refresh rate of at least 60 Hz or more is required (in a non-interlace mode) to avoid the human eyes from feeling flickering.
Hence, when the motion picture data is displayed via the VGA controller, the vertical sync frequency of the motion picture data written in the video RAM is often different from the refresh rate for screen display. In such case, so-called xe2x80x9ctearingxe2x80x9d occurs, i.e., a horizontal line seems to scroll from the top to bottom or vice versa on the display screen. The xe2x80x9ctearingxe2x80x9d is produced as follows.
For example, assume that the vertical sync frequency of the motion picture data is 60 Hz (60 fields/sec), and the refresh rate for screen display is set at 75 Hz. In this case, the field image of the motion picture on the video RAM is refreshed 60 times per sec by writing the motion picture data, while the number of fields to be read out from the video RAM to refresh the screen is 75 per sec. Hence, a field image in the middle of being rewritten on the video RAM is read out, and is displayed as the next field, thus causing the above-mentioned xe2x80x9ctearingxe2x80x9d.
Also, since the motion picture data premised on a display on a home TV and computer graphics data have different color spaces, signal bands, scan schemes, and the like, the VGA controller must convert the color space of the motion picture data from YUV into RGB for computer graphics, and must perform other conversion processes such as conversion of the signal band (conversion of the dynamic range), conversion from the interlace mode to the non-interlace mode, and the like. Conventionally, independently of the display monitor or TV on which the motion picture data is to be displayed, the motion picture data is temporarily written in the video RAM. Hence, such conversion processes are performed not only when the motion picture data is displayed on the display monitor of the computer, but also when it is displayed on the TV. For this reason, when the motion picture data is displayed on the TV via the VGA controller, the displayed image is inferior to the original image as a result of various conversion processes.
It is an object of the present invention to provide a display controller, computer system, and motion picture display control method, which can prevent the above-mentioned xe2x80x9ctearingxe2x80x9d and deterioration of image quality that may take place when motion picture data is displayed on a TV, and can display motion picture data such as a DVD title and the like with high quality.
In order to achieve the above object, according to the present invention, there is provided a display controller which can display an image on a display monitor of a computer having an image memory or a TV, comprising: a port for externally inputting motion picture data; and refresh rate control means for matching a refresh rate used for displaying the motion picture data input from the port on a screen of the display monitor or TV with a vertical sync frequency of the motion picture data input from the port.
According to this display controller, when motion picture data is input from the port, the refresh rate is automatically changed in correspondence with the vertical sync frequency of that motion picture data. As a result, the number of field images of a motion picture to be refreshed per second by writing motion picture data in the image memory can be matched with the number of fields to be read out from the image memory and displayed per second for refreshing the screen, thus preventing the above-mentioned xe2x80x9ctearingxe2x80x9d. Hence, even when motion picture data is temporarily written in the image memory and is then displayed on the display monitor, the user can observe a high-quality image free from xe2x80x9ctearingxe2x80x9d.
Since the refresh rate is changed in correspondence with the vertical sync frequency of the motion picture data, the horizontal/vertical sync signals of the motion picture data input from the port can be used as those for displaying on the display monitor or TV. Since the horizontal/vertical sync signals of the motion picture data input from the port are used as those for displaying on the display monitor or TV, mapping of motion picture data on the image memory can be perfectly synchronized with refreshing. More specifically, even when the refresh rate is concordant with the vertical sync frequency of the motion picture data, a horizontal line may appear at a specific position in the display screen if phase shifts are present. However, since mapping of motion picture data on the image memory can be perfectly synchronized with refreshing, such problem can also be solved.
Also, according to the present invention, a display controller which can display data written in an image memory on a display monitor of a computer or a TV, comprises a port for externally inputting motion picture data, and a transfer bus inserted between the port and a TV encoder for generating a TV video signal, and is characterized in that when the motion picture data input from the port is displayed on the TV, the motion picture data is directly transferred from the port to the TV encoder via the transfer bus.
In this display controller, the transfer bus is prepared as a route for directly inputting the motion picture data from the port to the TV encoder. When motion picture data is displayed on the TV, the motion picture data from the port is directly sent to the TV encoder without the intervention of an image memory, and is displayed on the TV. With this arrangement, the need for conversion processes such as conversion of the color space of the motion picture data from YUV to RGB for computer graphics, conversion of the signal band (conversion of the dynamic range), conversion from the interlace mode to non-interlace mode, and the like can be obviated, and deterioration of image quality due to such conversion processes can be prevented.
Even when such pass through mode without the intervention of an image memory is used, since the horizontal/vertical sync signals of the motion picture data are directly sent from the port to the TV encoder together with the motion picture data, the horizontal/vertical sync signals of the motion picture data input from the port can be directly used as those for displaying on the display monitor or TV.
A switch means for switching data to be input to the TV encoder between motion picture data transferred via the transfer bus and display data read out from the image memory is preferably arranged at the input stage of the TV encoder. When the TV encoder input is switched to the transfer bus side by the switch means, the motion picture data can be directly displayed on the TV. On the other hand, when the TV encoder input is switched to the image memory side, graphics data mapped on the image memory by an application program can be displayed on the TV. Furthermore, the graphics data on the image memory and the motion picture data can be synthesized and displayed by switching the input by the switch means, and even when the transfer bus is used, overlay display for displaying motion picture data on a window which is opened at a specific position on the graphics field can be implemented.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.